The U.S. military had unusually strong words for Beijing over social media on Saturday after recent reports that an American reconnaissance plane had been warned to "leave immediately" during a flight near China's man-made islands in the contested South China Sea.

Reporters with CNN and the BBC had been given a rare chance Friday to look at the islets in the Spratly chain of the waterway from aboard a U.S. Navy P-8A Poseidon at 16,500 feet.

During the flight, reporters were shown four low-lying coral reefs in the Spratlys — Subi Reef, Fiery Cross Reef, Johnson Reef and Mischief Reef — three of which were turned into garrisons with massive radar installations, scores of buildings and military-grade runways. The crew received six separate warnings from the Chinese military, telling them they were inside Chinese territory and urging them to leave, CNN reported.